It is known that add a sense resistor may be used to monitor current through an electrical-load by monitoring the voltage across the sense resistor, and detect fault conditions based on the current measured. In the case of an open-circuit (OC) fault or short-to-ground (STG) fault condition, nearly zero current will flow through a switching-device that controls the electrical-load during the on-state of the switching-device. Undesirably, a current monitoring circuit is required along with a current sensing device (e.g. the sense resistor). Furthermore, current monitoring circuits for detection of an open load condition that utilize external sense elements and signal amplifiers (such as a low value sense resistor) are expensive and consume valuable printed circuit board space. Also undesirably, detecting an OC fault while the switching-device is in an on-state typically requires system level (behavioral) diagnostics, information that is typically not communicated to a controller configured to detect fault conditions in a circuit that operates an electrical-load.
Integrated drain-to-source voltage (VDS) sensing methods of external field effect transistor (FETs) are typically not effective when the mathematical product of the on-state current (drain current ID) and on-resistance (Rdson) of the FET (i.e. the switching-device) is relatively low in magnitude. The drain current flowing through a typical external FET fails to develop a sufficient voltage from drain-to-source to enable reliable detection. Integrated Sense-FETs are expensive and are also relatively insensitive with respect to their ability to differentiate operating current from an open circuit. Alternative high “ON-Resistance” solutions have undesirably high static power dissipation.